Table V.
Recovery of Sulfur-35 from Seawater
SamPle
Sulfur-35, D.P.M. Found KO. Taken 1 8 . 2 X 10’ 8 . 3 X 1 0 ’ 5 5.170 2 8 . 1 x 103 7 . 9 x 103 i 5.470 3 1.62 X l o 4 1.47 X l o 4 i 3.1y0
Table VI. Decontamination Factors of Various Radionuclides in Y5Procedure
Radionuclides
Decontamination Factor
> 107 > 107 2107 107
>I06 >io7
1106 > 106
105
Mixed Fission Products (18 days old)
> 106 >107
RESULTS AND DISCUSSION
Sulfur-35 Procedure. T h e initial treatment of the sample with hydrogen peroxide oxidizes a n y hydrogen sulfide t o sulfate ion and ensures complete exchange between 5 3 5 and its sulfate carrier. Bush ( I ) reported that with concentrated sulfuric acid and excess concentrated hydrogen iodide the reaction
product is mainly hydrogen sulfide according to the equation 2H’
+ SOL-* + 8HI
-+
Hi3
+ 412 + 4HzO
However, it is posbible to obtain sulfur dioxide if the HI is slightly diluted. The results of measurements of recovery of known amounts of S35 introduced into seaiyater are presented in Table V. The usual corrections n-ere applied for chemical yield and counting efficiency corresponding to the n-eight of barium sulfate precipitate recovered. Each value represents the average of triplicate determinations, and the precision of such determinations was about = ! ~ 5 7 ~Errors ,. are due mainly to difficulties in obtaining barium sulfate precipitate mounts which were sufficiently reproducible for precise counting of the weak beta-rays of S35. This problem can be partially eliminated by adopting the procedure for assaying S36through gas counting (12) or liquid scintillation counting (9) techniques. The procedure gives decontamination factors of >IO7 from mixed fission products (Table VI), chemical yields of 70 to 80%, and a precision of about &5%. This procedure is also adaptable to the simultaneous determination of a large number of samples. LITERATURE CITED
(1) Bush, F., J. Phys. Chem. 33, 613 (1929). (2) Charpie, R. A., Dunworth, J . V., ed., “International Series of Monographs on Nuclear Enerev: Phvsics of Nuclear Fission,,, p. 75, &gam& Press, 1958. (3) Conner, R. D., Fairweather, I. L.,
[’roc. Phys. SOC.(London) 70A, 769 (1957). ( 4 ) Covell, D. F., ASAL. CHEM.31, 1785 (1959); U. S. Naval Radiological Defense Laboratory Technical Rept., USNRDL-TR-288, December 1958. (5) Dyrssen, D., Nyman, P. O., Ada Radiol. 43, 421 (1955). (6) “Effects of Atomic Radiation on Oceanography and Fisheries,” Publication KO.55, National Academy of Sciences, National Research Council, Washington, D. C., 1957. (7) Handley, T. H., Reynolds, S. *4., Oak Ridge National Laboratory, CF-56-7118, July 23, 1956. ( 8 ) Harvey, H. W.,“The Chemistry and Fertility of Seawater,” p. 9, Cambridge University Press, Cambridge, 1960. (9) Jeffay, H., Olubajo, F. O., Jewel], W.R., AXAL.CHEW32, 306 (1960). (10) Katcoff,S., A‘ucleonics 18,201 (1958). (11) Knowles, J. IT., Can. J . Phys. 37, 203 (1959). (12) Merritt, W. F., Hawkings, R. C., ANAL.CHEK 32, 308 (1960). (13) Metcalf, R. P., “Radiochemics;! Studies, The Fission Products, Book I, C. D. Coryell, N. Sugarman, eds., National Nuclear Energy Series, Paper No. 47, p. 478, McGraw-Hill, 1951. (14) Pate, B. D., Yaffe, L., Can. J . Chenz. 33, 610 (1955). (15) Prestwood, R. J., “Collected Radiochemical Procedures,” LA-1721, 2nd ed., J. Rleinberg, ed., Los Alamos Scientific Laboratory, Los Alamos, August 1958. (16) Seliger, H. H., Mann, W.B., Cavallo, L. M., J . Research AJatl. Bur. Standards 60, 447 (1958). (17) Senftle, F. E., Champion, W. R., Nuovo Cimento, Suppl. 12, 549 (1954). (18) Sreb, J. H., Phys. Rev.81,469 (1951). (19) Willard, H. H., Furman, N. H “Elementary Quantitative Analysis,;’ pp. 363 ff., Van Nostrand, New York, 1940.
RECE~VED for review September 11, 1961. Accepted January 2, 1962.
Radioassay of Metha nethio I-S u Ifur- 35 a nd Methanethio I-Ca rbon- 14 ROLFE H. HERBER Ralph G. Wright Laboratory o f Chemistry and the Nuclear Science Center, Rutgers, The State University, New Brunswick,
b A method for the radioassay of sulfur-35-labeled methanethiol is based on the precipitation of the mercuric salt of the methyl sulfide anion when the labeled mercaptan is transferred by high vacuum gas handling techniques into an aqueous solution of mercuric cyanide. The precipitates are filtered into M-grade sinteredglass crucibles, washed with distilled water and 95% alcohol, and then dried to constant weight a t 85 =t 5 ” C. Radioassay of the precipitates which have been prepared in layers of uniform thickness is carried out 340
0
ANALYT!CAL CHEMISTRY
using a thin-window gas flow counter, Correction factors for the self absorption of the soft beta radiation in the samples have been determined and good reproducibility of specific activity has been obtained. This method is equally applicable to the radioassay of methanethiol-carbon-14.
I
an investigation (9, 11) of the chemical consequences of the Cl35 ( ~ , P ) Sreaction, ~~ i t has been found t h a t when thermal neutron irradiated hexachloroethane is scavenged under N
N. 1.
high vacuum conditions with methanethiol, sulfur-3&labeled CH3SH can be obtained. The quantitative study of such hot atom reactions requires the exploitation of a reproducible radioassay technique for the sulfur radioactivity which is produced. Due to the low energy (Emax, = 0.167 m.e.v.) (4) of the S35radiation, gas phase radioassay methods ( I , 10, l 4 , 1 6 ) which have been developed for the quantitative determination of (2186, Br*Q,1’28, P3*, and other “hard” beta emitters, cannot be employed in the present case. Alternatively, a number
~
methods have been proposed (6-12, 15) for the radioassay of weak beta emitters by scintillation techniques. While these methods are frequently rapid and convenient, the cost of the appropriate equipment is considerably greater than that for solid sample beta radioassay with a GeigerRluller counter. Since such counters are commonly available in laboratories in which radionuclides are used, a method for the radioassay of CH3SH (labeled either Kith CI4 or S3jj in the form of solid samples has been developed, and is here reported. Although a number of methods have been suggested for converting the sulfur atom of the methanethiol to barium sulfate, these methods (5, 17) tend in general to be time consuming and of low intrinsic chemical efficiency. Previously reported methods (17) have exploited the low solubility of (CH3S)Ag as a separation technique in the study of isotopic exchange reactions. However, the subsequent conversion of the sulfur atom of the silver salt to BaS04 counting samples involves fusion in a nickel crucible in a mixture of KKO1 and Na2C03and subsequent leaching of the product Tvith water to permit precipitation of the barium salt. Such a procedure is both time consuming and inconvenient for a large number of samples. In this investigation, a number of methods were attempted to oxidize quantitatively small quantities of the S(I1) atom in CHBSH to S(V1) using bromine, permanganate, and aqua regia as oxidizing agents. I n no instance could recovery of sulfate as BaSOr be achieved n i t h good reproducibility. A more convenient method of preparing a solid counting sample of CH3SH is based on the insolublity of the mprcuric salts of the thiol in aqueous solution. P\Ionothiol salts can be obtained (Z, 3) b y treating methanethiol with mercuric chloride. while the dithiol salts can be formed ( I S ) by using mercuric cyanide as a precipitant. The considerable solubility of Hg(CN)* in organic solvents is also advantageous in isolating the thiol from mised solvents such as alcohol-mater and acetonewater mistures should experimental conditions so require.
~~
of
EXPERIMENTAL
To test the suitability of using solid samples of dimethanethiol mercury(I1) in the radioassay of CH3S35H,a standard vacuum line procedure was employed. Small known quantities (0.2 to 1.0 mmole) of the thiol, which had been stored in all-glass ampoules over mercury, were dosed from a precalibrated volume a t known temperature and pressure into liquid nitrogen-cooled cold finger containing 10 ml. of aqueous saturated Hg(CK)2 solution. The cold finger was sealed off and allowed to
Table I.
Time Interval (Min.) 60 1200 15
30 100 1200 2640
Total Time Conditions CaClz desicc.
(Min.)
60 1260 1275 1305 1405 2605
1
1.4817 1.2101 0.9674
85 f 5" C.
o. . 4168 ~ 0.4017 0.3992 0.4016
5245 Table
Sample Planchet Mg. sample Ket activitv, c.p.m. C.p m./mg.
Drying of Precipitates
Self abs. corr. Corrected c p.m /mg.
II.
Net Weight (Grams) Sample 2 3 1.3301 1.2711 1.0467 0.9750 0.8753 0 7632 40013 o. 2816 ~o . _ 0.2878 0.2791 0.2841 0,2778 0.2870 0.2785
4 1.3813 1.0395 0.7802 n. 2814 0.2791 0.2778 0.2785
Counting Data
B
A
2 2 55 8 442 55 6 1 143 X l o 4 1 135 X lo4 175 4 205 257 3 16 0 399 0 501 0 416 514 5 13 7 60 1
warm to room temperature. On melting, the ice slush immediately gave rise t o a white precipitate which had a somewhat curdy noncrystalline appearance. The cold fingers were opened and the precipitates transferred quantitatively with distilled water into beakers and thence again with distilled n-ater into preweighed, RI-grade sintered-glass crucibles. The precipitates were washed with about 5 ml. of 95% E t O H and the crucibles transferred first to a CaClz desiccator and then t o an S5 + 5' C. drying oven. The net weights of a typical set of samples subjected to this treatment are summarized in Table I. These data show that while desiccator drying at room tpmperature removes only a small portion of the absorbed solvents and is thus ineffective for these samples, drying a t 85 =t5' C. for about 60 minutes yields a n essentially constant weight sample. The reproducibility of sample weights for 5 samples was zt0.427, indicating quantitative recovery of the mercuric salt. A sample of the oven-dried solid was covered with a water-moistened filter paper overnight and rweighed without further treatment. The weight gain was +0.051% showing that the solid is not a t all hygroscopic and hence can be stored without special desiccation even in humid atmospheres. Washing of a 400-mg. sample of the precipitate with IO-ml. aliquots of 95% alcohol followed by drying a t 85 f. 5" C resulted in a weight change of less than 0.8 mg. per washing. Thus small quantities of ethyl alcohol can be employed in li-ashing the precipitate free of n-ater without causing appreciable sample loss. Elemental analysis for carbon, hydrogen, and sulfur was carried out on a sample of the (inactive) dried precipitate. The results of this analysis are consistent with the identification of the white precipitate as the dithiol salt, and no further qualitative deterniination on the precipitate was deemed required. The counting samples were prepared in the standard manner by suspending
C 4
5
I3
60 2 176 2 2 93 0 390 7 51
87 0 183 5 2 24 0 308 7 27
56 6 162 6 2 87
0 310 7 00
a small amount of the precipitate with 95% ethyl alcohol and transferring this slurry t o preweighed stainless steel planchets of 2.4 em. diameter. Drying the slurry under a n infrared heat lamp gave rise to curdy uneven layers of solid. Much better counting samples were obtained b y drying the slurries at 85 f 5' C. in a drying oven, and allowing the planchcts to cool to room temperature while stored in covered Petri dishes. Radioassay of the samples was carried out using a gas flow counter. This counter has a volume of about 30 cc. and a n anode of 2-mil stainless steel. The 3-cm. diameter window is of 0.5 mil doubly aluminized Mylar (obtained from Coating Products Co., Englewood, N. J.). Using a counting gas of 99.05% helium-O.95% isobutane the detector was operated in the Geiger region at 1080 volts. The over-all dtttction efficiency for this counter with the source approximately 1 em. from the windolv was determined for calibrated sources of C14 (0.155 m.e.v.), T1204(0.764 m.e.v.), and Bizlo (1.155 m.e.v.). Interpolation for the S35 beta radiation gave an over-all detection efficiency of 6.5 i 0.5%. Typical counting data are summarized in Table 11. Since the S35 was produced from Cl3j under conditions which also produce P32in the target material [by the CIS5 (%,a) reaction], and since the cooling period of the target was insufficient to reduce the phosphorus activity (half life 14.30 days) to negligible values, i t mas important to ascertain the radiochemical purity of the counting samples. I n view of the relathe hardness of the P32beta (E,,,, = 1.712 m.e.v.) this is most readily doiie by aluminum absorption measurements. The half thickness for the S35 beta activity was 2.48 i 0.05mg. em.? of aluminum from data extending over 10 half thicknesses. The S35to P32ratio \+as determined from these data to be greater than 104, VOL. 34, NO. 3, MARCH 1962
a
341
DISCUSSION AND SUMMARY
Table 111.
hIg. Cm.-2 0 2
4 6
8
IO 12 14 16 18
Self-Absorption Correction Factors
(CH3S36)2Hg
BaS3604
1,000
1,000 0 896
0.880 0.764 0.656 0.565 0.487
0,425
0.375 0.338
0,792 0,704 0.624 0 552 0.492 0,440 0.396
20 22 24
indicating that the precipitation-mashing procedure ensures adequate cleanup from any adsorbed P32activity which may have been present. The self-absorption correction factors used in the calculation of the data in Table I1 were determined independently from eight samples covering a thickness range from 2.79 to 18.13 mg. The self-absorption correction data taken from a smoothed line plot are summarized in Table 111. I n this table are also given the corresponding correction factors for BaS3j04radioassayed under identical conditions. A semilogarithmic plot of the apparent specific activity as a function of sample thickness gives a good straight line plot with a half thickness of 9.95 i 0.10 mg. (CH3S)ZHg per sq. em. The corresponding value for Bas04 is 11.80 =t0.10 mg. cm,-2
From the above data it is seen that the precipitation of the dimethanethiol mercury(I1) salt from a n aqueous solution of mercuric cyanide on the addition of CHISH is a convenient method for the radioassay of the sulfur-35 labeled thiol. Because of the nature of the precipitate, no digestion period is required in the preparation of the samples. Under routine laboratory conditions, a complete radioassay should be possible in 2 to 3 hours. The method here reported has been employed in a study (11)of the chemical consequences of the C13j(n,p)S35 reaction in volatile halide targets such as CC11. An obvious advantage in this application is the ease of effecting a qualitative separation of dimethanethiol mercury(I1) from other sulfur activity carriers such as sulfide, sulfite, and sulfate. Since the maximum beta energy of CI4 (0.155 m.e.v.) is close to that of S3j, this method finds an obvious estension to the radioassay of C14H3SH. Since the C14 beta radiation has an over-all counting efficiency in our experimental arrangement of 5.667, (based on standardization with a calibrated source), an independent self-absorption correction curve for the C14-labeled (CH$)2Hg is required for quantitative radioassay of these samples. ACKNOWLEDGMENT
The author is indebted to S . S. Sugarman of the University of Chicago for the detailed draxvings of the endwindoiv flow counter and to Bernard
Serin for assistance with its construction. The elemental analyses were carried by George Robertson. LITERATURE CITED
(1) Adams, R. RI., Bernstein, R. B., Kats, J. J., J . Chem. Phys. 23, 1622 (1955). (2) Blackburn, S., Challenger, F., J . Chem. Soc. 1938, 1867. (3) Challenger, F., Rawlings, A. A,, Ibid., 1937, 868. (4) Connor, R. D., F a h e a t h e r , I. L., Proc. Phys. SOC.(London) 70A, 679 11957). (5) Fava, A., Iliceto, A., Camera, E., J . i l m . Chem. SOC.79, 833 (1957). (6) Funt, B. L., Hetherington, A., Science 129, 1429 (1959). (7) Hayes, F. N., Rogers, B. S., Langham, W.H., Arucleonics 14(3), 48 (1956). (8) Helf, J., Castorina, T. C., White, R. G., Graybush, R. J., ASAL. CHEM. 28, 1465 (1956). (9) Herber, R. H., J . Inorg. 4uclear Chem. 16, 361 (1961). (10) Herber, R. H., Rev. Sei. Instr. 28, 1049 (1957). (11) Herber, R. H., Proc. S y m p . Chemieal Effects of Nuclear Transformatzons, Prague, October 1960; I.A.E.A. p. 201, Vienna, 1961. (12) Meinke, K.FV., BXAL.CHEX 32, 104R (1960). (13) Sakamura, N., Baochem. 2. 164, 31 (1925). (14) Sorris, T. H., J . Am. Chem. SOC. 74, 2396 (1952). (15) Radin, N., Fried, R., ANAL.CHEM. 30, 1926 (1958). (16) Rogers, M. I., Kats, J. J., J . Am. Chem. SOC.74, 1375 (1952). (17) Sehon, ,4.H., Darwent, B. De B., Ibzd., 76, 4806 (1954).
RECEIVEDfor review August 9, 1961. Accepted December 4, 1961. Research supported in part by the U. S. Atomic Energy Commission and the Suclear Science Center, Rutgers, The State University.
Counting of Alpha- and Beta-Radiation in Aqueous Solutions by the Detergent-Anthracene Sci nti I latio n Method L.
S. MYERS, Jr., and A. H. BRUSH
The laboratory of Nuclear Medicine and Radiation Biology of the Department of Biophysics and Nuclear Medicine, and the Department of Radiology, School of Medicine, Universify of California, Los Angeles, Calif.
b The use of a two-phase solutiondetergent-anthracene system as a general method for counting CY- and @-radiation in aqueous solutions is proposed. The method consists of pipetting the radioactive solution onto detergent-coated anthracene in a vial and counting in a liquid scintillation counter. Counting efficiencies depend on the radiation energy and, for all except the weakest radiations, are 50 342
ANALYTICAL CHEMISTRY
to 100%. Inorganic solutes in up to 1 M concentration and water-soluble organic solvents do not interfere, and hence nearly all sample preparation steps can b e eliminated. A tendency for the detergent to foam, and sorption of the isotope onto the anthracene may influence results under certain conditions. This difficulty can be controlled, however, by regulating the p H and ionic strength,
R
ADIOCHEMICAL
AKALYSIS
Of
aqueous solutions ITould be greatly facilitated by the development of a good method of counting cy- and j3emitting isotopes in solution. I n a n attempt to find such a method an extensive study has been made of the properties of the ho-phase solutiondetergent-anthracene scintillation system-first suggested by Steinberg primarily for counting CI4 in compounds
